Classical class I molecules present endogenous peptide antigens for recognition by cytotoxic T lymphocytes. Nonclassical class I (class Ib) molecules, although similar in structure to classical class I molecules, have an unknown function. In this project we are studying the cell biology biochemistry, and function of two representative mouse class Ib molecules, Q7b and mCD1.1, with the ultimate goal of determining the role of these molecules in anti-viral immune responses.